Direct SPD-processing to achieve high-ZT skutterudites

Author(s)
G. Rogl, A. Grytsiv, R. Anbalagan, J. Bursik, M. Kerber, E. Schafler, M. Zehetbauer, E. Bauer, P. Rogl
Abstract

For mass fabrication of thermoelectric generators a fast, cheap and simple method is required to produce high Zr leg material. It is well known that severe plastic deformation (SPD) enhances the density of defects and dislocations, and also refines the grains to nano-size. These are the essential key parameters for low thermal phonon conductivity. Consequently and as a first example, SPD via high-pressure torsion (HPT) at elevated temperatures in protective gas atmosphere was used to directly consolidate and plastically deform commercial p-type skutterudite powder, DDyFe3CoSb12, (DD stands for didymium) into a dense thermoelectric solid. The HPT-sample exhibited a high figure of merit, ZT > 1.3 at 773 K, much higher than that of the hot-pressed reference sample (HP) from the same powder. The Zr achieved is comparable with ZTs of corresponding high energy ball milled and hot pressed samples (HBM-HP) as well as of ball milled, hot pressed plus HPT processed skutterudites (BM-HP-HPT). The thermoelectric efficiency is even 4% higher. Synchrotron measurements were performed at temperatures from 300 to 825 K in order to evaluate the changes in grain size and dislocation density of the CP-HPT samples before, during and after annealing. SEM and TEM images served to give a better insight into the temperature dependent diversification of the new material. Due to grain refinement and enhanced dislocation density, the CP-HPT material exhibits higher hardness values than the reference sample. The elastic moduli are, within the error bar, the same.

With large high-pressure torsion facilities at hand, a new, fast and therefore cheap mass production of thermoelectric leg material directly from powders can be envisaged. This new production technique furthermore warrants high figures of merit but excludes time-consuming ball milling and hot-pressing steps. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Organisation(s)
Department of Materials Chemistry, Physics of Nanostructured Materials
External organisation(s)
Academia Sinica - Taiwan, Czech Academy of Sciences, Christian Doppler Laboratory for Thermoelectricity, Technische Universität Wien
Journal
Acta Materialia
Volume
159
Pages
352-363
No. of pages
12
ISSN
1359-6454
DOI
https://doi.org/10.1016/j.actamat.2018.08.020
Publication date
10-2018
Peer reviewed
Yes
Austrian Fields of Science 2012
Materials chemistry
Keywords
Portal url
https://ucris.univie.ac.at/portal/en/publications/direct-spdprocessing-to-achieve-highzt-skutterudites(3e8eef47-01a5-4c60-824e-26f6872a0442).html